Known in the prior art are the stands of a cold tube-rolling mill comprising a housing with two pairs of uprights located between which are the work rolls with bearing supports installed on both sides of the work rolls, and between each pair of circular passes and interconnected in pairs with a certain prestressing by tie bolts (Pat. No. 1,287,541, Federal Republic of Germany). In such stands the radial rolling forces are transmitted by the bearing supports to the tie bolts, while the provision of additional bearing supports located between each pair of passes and likewise held together with bolts with a certain prestressing counters the sagging of the rolls.
In these stands the prestressing of the work rolls is changed and controlled by tightening the bolts; this calls for stopping the mill and involves a considerable waste of time. Besides, the diameter of the bearing supports taking the rolling forces in this design depends on the diameter of the work roll. The rolling of extra-thin-walled tubes and small-diameter tubes from hard-to-work metals and alloys under advanced technological conditions calls for the use of sets of small-diameter work rolls (100-200 mm) in order to rule out the effect of flexible flattening of the work rolls on the thickness of the tube wall and the accuracy of the rolled tubes and to reduce the contact zone between the metal of the tube being rolled and the work rolls since a large contact zone results in considerable heating of the tube billet and tool (particularly the plug and the internal layers of metal of the tube billet due to an insufficient abstraction of heat by the cooling fluid) which intensifies the sticking of metal to the tool, impairs the quality of the rolled tubes and aggravates the tool wear. The life of the bearing supports of the work rolls is short due to the considerable radial forces arising in the rolling of tubes from hard-to-work materials.
At present one can witness certain tendencies towards perfecting the stands of the cold tube-rolling mills by introducing backup rolls which take up all the rolling forces.
Such a stand of a cold tube-rolling mill comprises a housing with uprights arranged in pairs opposite to the axis of rolling, work rolls installed one above the other in bearing supports between the lower and upper backup rolls mounted in the corresponding bearing chocks adapted for vertical setup motion, and a device for a positive contact of the work rolls, said device having the form of a common cover articulated to the uprights by axles and wedge mechanisms for its vertical setup motion and provided with a stop in the form of a bearing bar which is in positive contact with the upper backup roll (Author's Certificate Int Cl. B21B 21/00 No. 365090, USSR).
In this stand of the cold tube-rolling mill the radial rolling forces are taken by the backup rolls while the provision of wedge mechanisms for the vertical setup motion of the cover makes it possible to install the work rolls with a certain prestressing which is accomplished as follows. The wedge mechanisms move the cover vertically down whereas the force is transmitted by the bearing bar and the upper backup roll to the work rolls, the lower backup roll and, via the lower bearing bar and the base to the housing uprights.
However, the layout of the device for the positive contact of the work rolls in the form of a common cover and wedge mechanisms which articulate said cover with the uprights hinders the process of adjustment and denies the possibility of prompt and accurate setting of the preliminary radial force of clamping of the work rolls because the vertical position of the cover is set with the aid of separately installed wedge mechanisms. Moreover, in this stand it is impossible to change the prestressing of the work rolls in the course of mill operation. For fitting this stand with sets of work rolls of a different diameter it is necessary to replace the backup rolls, gearing elements and bearing bars which also involves considerable waste of time and the provision of additional structural elements.
An object of the present invention resides in providing a stand of a cold tube-rolling mill which would ensure uniform clamping of the work rolls by the backup rolls with the required force throughout the length of their contact.
Another object of the present invention resides in providing a stand of a cold tube-rolling mill which would permit changing the prestressing of the work rolls in the course of operation.
And still another object of the present invention resides in providing a stand of a cold tube-rolling mill which would permit installation of sets of work rolls of different diameters for rolling tubes of different gauges from hard-to-work materials.
The essence of the present invention lies in providing a stand of a cold tube-rolling mill, consisting of a housing with pairs of uprights arranged opposite to the axis of rolling, of work rolls installed one above the other in bearing supports between pairs of lower and upper backup rolls mounted in corresponding bearing chocks of which the upper ones are adapted for vertical setup motions and a device for a positive contact of the work rolls wherein, according to the invention, the device for the positive contact of the work rolls has a leverage or linkage mechanism for each bearing chock of the upper backup rolls, said linkage mechanism linking kinematically the bearing chock with an independent power drive for ensuring the vertical setup motions of said chock.
It is practicable that the linkage mechanism should be made in the form of a beam, one end of which is articulated with one upright of the pair, has a stop which is in positive contact with the bearing chock of the upper backup rolls, a rod and an eccentric shaft, said elements linking kinematically the other end of the beam with the other upright of the pair and with a movable member of an independent power drive.
Such technical solutions permit fitting the stand with sets of work rolls of different diameters without replacing the backup rolls and ensure uniform clamping of the work rolls by the backup rolls with the required force along the length of the contact by means of the setup motion of the upper backup rolls through their bearing chocks with the aid of the device ensuring the positive contact of the work rolls.
It is practicable that the bearing support of each work roll should be made in the form of a spherical joint installed in the support body with a clearance intended to make up for the errors occurring during the setup motions of the bearing chocks of the backup rolls.
Moreover, such technical solutions will improve the accuracy of setting of the work rolls, and the rigidity of the system: work rolls--bearing chocks--uprights--stand housing and thus will raise the accuracy of the thin-walled tubes and of the tubes from hard-to-work materials rolled in this stand.